If you’re the parent of a Boston public school student, perhaps one who is in school at this very minute, you already know what the surprise was: The last day of school is officially Wednesday.

Well, sort of. Some schools, parents said, had made it clear that attendance on Tuesday and Wednesday was more or less optional, with absences not counting against their children’s already completed report cards or not recorded at all. Add that to the hassle of half-days Tuesday and Wednesday, which means providing care for children at odd hours, and summer came early for more than 30 percent of Boston public school students.

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“I was shocked,” said Andrews, who decided not to bother with the half-days scheduled for Tuesday and Wednesday. “It’s a waste of time.”

Wednesday marks the 180th day of classes for Boston public school students, the minimum number allowed by the Massachusetts Department of Elementary and Secondary Education. The 180-day requirement is aimed at ensuring that students in every district get enough learning time in classrooms. But the difficulty of finding day care for a half-day — and some schools’ laissez-faire attitude toward attendance this week — has led parents like Andrews to skip the school year’s final bell.

At least 19,000 of the 55,000 students in grades K-11 were not in school Tuesday, according to preliminary data provided by Boston public schools spokesman Brian Ballou (with graduation passed, seniors were already finished).

Waiting for his 9- and 10-year-olds outside Dever School Monday afternoon while a few students and teachers enjoyed the shady playground out front, Nguyen said he would not bother bringing them for the last two half-days, which amounted to about four hours of low-intensity class time.

“I’d just go home and come back,” said Nguyen of the trips to drop off and pick up his children. School starts at 9:30 a.m. at the K1-5 school on Mt. Vernon Street. On half-days, it lets out just two hours later, causing a bigger headache for parents like Andrews and Nguyen than it would be to find care for a full day.

Ballou acknowledged that the last couple of days of school are not always well attended, but he stressed that those students not in class Tuesday and Wednesday will be recorded as absent.

“We’ve instructed our schools that if a kid is absent, mark them absent,” Ballou said. “There has been no messaging to any of our schools to just casually take attendance these last days of the school year.”

He said Boston public schools are acting in line with state requirements. That policy dictates 185 days to be scheduled in every school year. Weather and other cancelations can drive that down to 180, but days beyond that must be made up.

“We expect all students to be engaged in structured learning time in school for a minimum of 180 days,” Jacqueline Reis, media relations coordinator at the Massachusetts Department of Elementary and Secondary Education, said in an e-mail.

‘Her teacher told me she can go if she wants to, but she doesn’t have to go.’

Some parents, though, are hearing a different message.

“Her teacher told me she can go if she wants to, but she doesn’t have to go,” said Min Yang, whose daughter Fanyi, 6, goes to Tynan Elementary School in South Boston and was planning to keep going through Wednesday.

Responses at several Boston public school offices contacted this week varied, with some saying attendance would be required and others saying the days were totally optional. “You didn’t even have to bring him today,” one front-office staff member at a Dorchester elementary school said when asked Monday, because report cards were already completed.

Other school officials indicated students who missed the last few days would be marked “constructively present,” a designation used to describe those who are not actually present. That designation was used last year for many students who stayed home when school remained open during a bad snowstorm.

“That’s not our policy . . . There is no districtwide message if a kid is absent to mark him as constructively present,” said Ballou, referring to the attendance code used “if a student is receiving school-related or instructional services outside of the building during the school day.”

About 600 students on any given day are marked constructively present, Ballou said, mostly because of alternative education programs and home hospital stays. Tuesday, the tally was 592, though that number was incomplete.

Other area districts finished earlier, and officials said attendance on the last day was partly driven by the day of the week. When school closes on a Friday, as it did in Newton, attendance tends to be higher. Closing mid-week — or finishing with a half-day on a Monday, as Cambridge schools did — is riskier.

Scheduling half-days for the end of the school year is routine, said Tom Scott, spokesman for the Massachusetts Association of School Superintendents. As for how many students around the state might be “constructively present,” he demurred.

“I’ve not heard that one,” Scott said. “I don’t know what that means.”

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